Worm Breeder's Gazette 8(3): 34

These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.

Dominant tra-2 Mutations and Sperm Whales

T. Doniach

Figure 1

One of the unsolved problems in understanding how genes control sex 
determination in C.  elegans is that of how spermatogenesis, a male 
function, occurs in the hermaphrodite, which is otherwise female.  The 
current model for sex determination can only explain how male vs.  
female development occurs.  As described in the last Newsletter, I 
have been working on several dominant tra-2 mutations that may bear on 
this problem.  These mutations eliminate spermatogenesis in XX animals,
to produce females instead of hermaphrodites, but do not generally 
show effects on XO males.  In the XX animal, tra-2 is thought to act 
with tra-3 to prevent the function of the fem genes.  In the XO 
animals, tra-2 appears to be turned off by the action of her-1, 
thereby allowing the fem genes to promote male development and 
spermatogenesis.  Since the fem genes are also needed for 
spermatogenesis in the XX animal, there must be a way of allowing them 
to promote a brief period of spermatogenesis without interfering with 
female somatic development or eventual oogenesis.
[See Figure 1]
The tra-2(dom) mutations indicate that this transient fem expression 
is mediated via the modulation of tra-2 activity.  That is, that 
although tra-2(+) is on in the XX animal, it is turned off transiently 
to allow the fems to promote spermatogenesis.  In tra-2(dom) animals, 
tra-2 activity is apparently no longer modulated, i.e.  it is 
constitutive, because tra-2(dom) XX animals are females.  However, XO 
tra-2(dom) animals are usually normal males, therefore tra-2(dom) is 
still turned off by her-1 in the XO animal.  In sum, in addition to 
the negative control of tra-2 activity by her-1 in the XO animal, tra-
2 is also modulated in the XX animal to allow hermaphrodite 
spermatogenesis to occur.  It is possible that genes that specifically 
control this modulation exist (indicated by the ? in model).
Two tra-2(dom) alleles, tra-2(e1940) and tra-2(e2020), have been 
characterized in greater detail.  Both have been reverted to yield 
several intragenic recessive masculinizing mutations that fail to 
complement tra-2(e1095) (a putative null).  This indicates that they 
are tra-2 alleles.
Although both mutations appear to be constitutive, their penetrance 
differs: tra-2(e1940) and tra-2(e1940)/+ XX animals are sometimes 
slightly self-fertile hermaphrodites instead of females, while tra-2(
e2020) and tra-2(e2020)/+ XX animals are always female.
Further, tra-2 activity appears to differ in the two alleles; tra-2(
e1940) activity is possibly lower than wildtype (hypomorphic) 
1) tra-2(e1940)/(e1095) XX animals are self-fertile intersexes in 
contrast to tra-2(+/e1095) XX animals, which are essentially wildtype 

2) the masculinizing effect of her-1(n695sd) is enhanced so that tra-
2(e1940)/+;her-1(n695)/+ XX animals are more intersexual than her-1(
n695)/+ alone.
By contrast, tra-2(e2020) does not appear to be a hypomorph because 
tra-2(e2020)/(e1095) XX animals are female, in both soma and germline. 
tra-2(e2020) activity may even be higher than wildtype (hypermorpic) 

1) tra-2(e2020);her-1(n695) XX animals are 
2) the masculinizing effect of the tra-3(e1767) mutation is 
partially suppressed so that tra-2(e2020)(/+);tra-3(e1767) animals 
will propagate slowly as a male/female strain.  This result is 
significant because it indicates that tra-2(e2020) can substitute for 
tra-3(+) function.
Another feature of tra-2(e2020) is that although tra-2(e2020) XO 
animals are morphologically male, they begin to produce oocytes and 
yolk (as judged by Nomarski microscopy) after spermatogenesis as 
mature adults.  This indicates that control by her-1 may have been 
somewhat affected in tra-2(e2020) XO animals.
In addition to indicating that the tra-2(dom) mutations affect XX-
specific control of tra-2 activity, these results show that the tra-2(
dom) mutations affect somatic as well as germline tissues.  The fact 
that in some circumstances these mutations appear to affect only the 
germline suggests that the soma and the germline may have different 
thresholds of sensitivity to tra-2 activity.
Dominant extragenic suppressors of tra-2(e1940) and tra-2(e2020) 
have been sought in the hope of identifying genes that act to modulate 
tra-2 specifically in the XX animal, allowing spermatogenesis.  No 
suppressors of tra-2(e2020) have been found, but tra-2(e1940) has 
yielded two so far.  Both are unlinked to tra-2(e1940) but are as yet 
unmapped.  These mutations produce a novel phenotype, the 'sperm 
whale' (Sw), which is a hermaphrodite whose gonad makes only sperm.  
One of them affects the soma as well as the germline so that tra-2(
e1940);sw/+ XX animals are self-fertile intersexes.  sw/+, sw/sw and 
tra-2(e1940);sw XX animals are sperm whales or hermaphrodites, with 
variable penetrance.
Finally, a mutation that appears to have germline-specific effects 
has appeared by chance in a suppressor hunt.  This mutation, e1959, 
which maps to the left arm of LGI, is recessive in XX animals, 
producing females, and has a semidominant feminizing effect on the 
germline of XO animals.  e1959/+ XO animals produce oocytes in a male 
gonad after a period of spermatogenesis, and e1959 XO animals often 
make only oocytes in a male gonad.  No yolk production is seen by 
Nomarski microscopy.

Figure 1